Calibration standards for glass bead x-ray fluorescence (XRF) analysis of geochemical samples are discussed in this article. Although rock references issued by geological organizations have often been applied to glass bead XRF, several problems remain: limited varieties and numbers, and uncertainty related to uncertified (recommended or preferred) values. Various geological references (e.g. rocks, sediments, and materials) having extensive elemental composition have often been applied for calibration. The XRF intensities must be corrected using an appropriate matrix-correction method because the matrix effect resulting from the application of various references was not negligible. Attempts have been made to extend the calibration range by geological reference with such approaches as blending some references and adding chemical reagents to references. However, geological references for the calibrating standards should be used intact because the reliability of the certified values of references is lost. Synthesized calibrating standards with chemical reagents have constitutive properties which are superior to those of the rock references. Synthesized standards can ensure the traceability of the analytical procedure and the resultant accuracy and propriety of calibration curves. Reliable calibration curves are obtainable by designing such parameters as the number of plots, plotting arrangements, and calibrating ranges. Synthesized standards must be prepared by fitting the elemental composition to each geological sample. This discussion reviews calibration standards applying rock references or chemical reagents related to glass bead XRF.
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